Blender 2.8 more gizmo!
From what I understand, yes it would make sense to make the gizmo appear when you press G, R or S, but it doesn't seem to be the case, you need to click on the Move, Rotate and Scale button on the Tools panel, which is a bit tedious.

One thing that is useful to know though is that you can choose to have the gizmo always displayed when you click on the gizmo's options on the bottom. In my opinion it's much more natural to keep it anytime like it was the case in 2.7.